This invention relates generally to surgically implantable prostheses and more particularly to endosteal implants. More particularly and definitively it relates to osseointegratable dental implants and prosthetic devices associated therewith It further relates to a process for preparing the implants and to a process for preparing the mandible or maxilla for reception of the implant and the prosthesis.
Dental implants are used when the patient, for various reasons, requires a prosthetic device to hold one or more artificial teeth in place. For example, the teeth surrounding the portion requiring the prosthesis may be too weak or far apart to provide adequate strength or bridging. The system available in the art largely involves the use of single, free-standing implants placed directly into the bone in the area as near to where the new tooth is needed as possible.
There are a variety of systems currently used and they are all based on the common feature of using a cylindrical shaped or screw-type implant tapped into the bone below the periosteum in either the maxilla or mandible. This cylinder or screw, which serves as the implant device, provides the basis for the support for the subsequently introduced artificial tooth or prosthesis via associated intermediate parts. For example, there are various pieces leading from the implant designed to be anchored into the implant and to lead ultimately out of the gum tissue. These are generally known as abutments. There are, for example, abutment cylinders held by abutment screws, one piece abutment/screw combinations, and other parts of varying designs that lead from the implant out of the bone through the gum and into the mouth. The generic term .THETA.abutment" will be in this specification to refer to the attachment assemblies to the implant that lead therefrom out of the gum and support the prosthesis. This abutment serves as a post and is adapted to receive the prosthesis which provides a support site for the artificial tooth. The implant over time becomes osseointegrated. That is, through natural body occurrences via osteogenesis, it actually integrates with the bone structure into which it is imbedded with concurrent formation of new bone, thus giving a very strong integrated connection to the bone.
Unfortunately, while these materials and implant systems have been successful in many cases, they have, for a variety of reasons, not reached the generally wide-spread use expected of them. One of these reasons is that the line of connection between the implant in the bone through to the artificial tooth is actually a straight line and is therefore subject to the potential for infection, fibrous encapsulation, and loosening. Since there is a direct connection from the prosthesis to the implant, bacterial infections can occur at that spot and proceed along the implant, and impede, disrupt, and reverse the osseointegration process. What results is a loosening of the implant in the bone structure and an ultimate failure of the system.
Another limitation presented by the current implant systems is that the single implant is not supported by other implants within the bone. Rather, mutual support gained by the joining of more than one implant, is obtained outside the bone via the prosthesis. The splinting effect of joining more than one implant by a prosthesis intraorally, is subject to fit inaccuracies which cause overloading of some implants and the underloading of others. There is no current method for implant prosthetics available for supporting more than one implant endosteally, that is, within the bone itself, presumably for the reason that it is very difficult to prepare an implant which can support a plurality of teeth, and yet at the same time be permanently and reliably affixed to or in the bone structure. Very often the anchoring of the implant is confined mainly to areas wherein the medullary or soft, spongy bone predominates, or sinus cavities and other structures prevent the necessary length required for strength. In the posterior residual alveda ridges there is little opportunity for attaching the implant to the compact bone structure and hence a precarious implant is obtained. Often, the location of the bone causes excessive angulation of the implant, leading to biomechanical overloading and failure.
Another disadvantage in the current system is that because of the direct line between the implant, abutment, and prosthesis, all of the force is directed onto a very small part of the bone.
The barriers preventing production of an implantable device capable of supporting many teeth have been many and severe. Until the present invention, there was no way to address bone with poor bone density, reduced height, or angulation, or spanning spaces larger than one tooth space. Indeed, prior to the invention, there has been no way to prepare an implant which rests within and is securely attached (integrated within) the compact bone, or to implant a device within the bone that can support more than one abutment which is splinted together within the bone and not dependent on the exact fit of an intraoral connection device for mutual support.